Oxidation of lipids produces an array of compounds, some of which are capable of mediating toxic reactions. It is hypothesized that specific oxidized lipids are also capable of activating cytoprotective pathways. Understanding how these responses are distinguished is critical in determining the molecular events that protect the cell against oxidative damage mediated by xenobiotics or during the pathophysiology of disease. Current thinking would suggest that oxidized lipids or lipoproteins are inherently toxic and therefore serve no useful function. However, the low, non-toxic concentrations of lipid oxidation products may well serve a protective function by activating signaling pathways that enhance antioxidant synthesis in the cell. This can then serve as an adaptive response as it increases the threshold at which oxidative stress and cytotoxicity occurs. Central in orchestrating the response of the normal cell to oxidative stress is the intracellular antioxidant glutathione. Little is known about either the endogenous control of synthesis of this antioxidant or its formation in response to oxidative stress. Preliminary data, which serves as the foundation for this proposal, show that exposure of endothelial cells to non-toxic mildly oxidized low density lipoprotein (oxLDL) is linked to the synthesis of GSH. An unknown signaling pathway leads to an increase in the concentration of intracellular GSH through enhanced activity of a rate-limiting enzyme involved in its synthesis, gamma-glutamylcysteine synthetase. Since it is well established that GSH plays a critical role in protecting cells against oxidative damage, this may be a mechanism through which the endothelial cell is protected by oxidized lipids. These data have led to the hypothesis that specific oxidized lipids generated during lipid peroxidation initiate transcriptional regulation of GCS and increase GSH synthesis. This hypothesis will be tested by pursuit of the following Specific Aims: 1) determine the effects of oxLDL on GSH biosynthesis in endothelial cells; 2) determine the transcription factor binding sites responsible for induction of GCS synthesis by oxLDL; 3) determine the lipid fraction in oxLDL that initiates induction of GSH synthesis by oxLDL. The information gained from the accomplishment of these specific aims will give insight into the mechanisms of antioxidant control in the cell and novel therapeutic interventions designed to modulate GSH in endothelial cells.